In order to create various light effects and mood lighting in connection with concerts, live shows, TV shows, sport events or as a part on architectural installation, light fixtures creating various effects are getting more and more used in the entertainment industry. Typically entertainment light fixtures create a light beam having a beam width and a divergence and can for instance be wash/flood fixtures creating a relatively wide light beam with a uniform light distribution or it can be profile fixtures adapted to project image onto a target surface.
Light emitting diodes (LED) are, due to their relatively low energy consumption, high efficiency, long lifetime, and capability of electronic dimming, becoming more and more used in connection with lighting applications. LEDs are used in lighting applications for general illumination such as wash/flood lights illuminating a wide area or for generating wide light beams e.g. for the entertainment industry and/or architectural installations. For instance like in products like MAC101™, MAC301™, MAC401™, MAC Aura™, Stagebar2™, Easypix™, Extube™, Tripix™, Exterior 400™ series provided by the applicant, Martin Professional A/S. Further LEDs are also being integrated into projecting systems where an image is created and projected towards a target surface, for instance like in the products MAC 350 Entour™ or Exterior 400 Image Projector™ also provided by the applicant, Martin Professional A/S.
Typically illumination devices based on LEDs comprises a multiple number of LEDs in order to achieve a high light output. In general it is desired to have illumination devices capable of illuminating very bright light beams and which at the same time is very energy efficient meaning that the light output pr. consumed power unit (e.g. measured as lumen pr. Watt) is as high as possible. However this is hard to achieve in projecting systems where the light in general is collected through an optical gate, which is imaged onto a target surface using an imaging optical system. Several attempts to achieve an effective LED based projecting device have been attempted, however further improvements in light output and efficiency is always desired.
WO0198706, U.S. Pat. Nos. 6,227,669 and 6,402,347 disclose lighting systems comprising a number of LEDs arranged in a plane array where a converging lens is positioned in front of the LED in order to focus the light, for instance to illuminate a predetermined area/gate or for coupling the light from the diodes into an optical fiber.
U.S. Pat. Nos. 5,309,277, 6,227,669, WO0198706, JP2006269182 A2, EP1710493 A2, U.S. Pat. No. 6,443,594 disclose lighting systems where the light from a number of LEDs is directed towards a common focal point or focusing area, for instance by tilting the LEDs in relation to the optical axis (JP2006269182 A2, WO0198706, U.S. Pat. No. 5,309,277) or by using individually refracting means positioned in front of each LED (U.S. Pat. Nos. 6,443,594, 7,226,185B, EP1710493).
WO06023180 discloses a projecting system comprising a LED array with a multiple number of LEDs where the light from the LEDs are directed towards a target area. The LEDs may be mounted to a surface of a curved base as or to a surface of a plane base.
Alternatively to the systems where the light from the light sources are directed directly along the optical axis several attempt have been made to create optical system where the light sources are arranged around the optical axis and where the light is emitted towards the optical axis in a direction substantially perpendicular to the optical axis and where a reflecting object is adapted to receive the light and reflect the light along the optical axis. For instance the following documents show such systems: JP2003347595, EP1466807, U.S. Pat. No. 7,237,927, GB2432653, EP2062295, EP2339224, EP2339225A, U.S. Pat. No. 7,891,840B. Commonly for these documents is the fact that the reflecting object is embodied as a cone or pyramid reflecting light form the light sources where the sides of the cone or pyramid reflect the light along the optical axes. However these systems are not very efficient as there is a relatively high loss of light due the fact that the top part of the light beams will pass the narrow top/tip of the cone or pyramid reflector rather than being reflected alone the optical axis. As a result these systems have a low light output pr. power unit. Further loss occurs when the common light beam is directed to an optical gate and later collected by a projecting system.
EP 0978748 discloses a multiple light source unit including:                a plurality of light sources for emitting light beams;        a condensing lens,        a mirror for directing the light beams from the plurality of light sources to the condensing lens; and        a light guiding element for receiving the condensed light beams through a light receiving section and for emitting the light beams through a light emitting section,wherein the light beams are parallel to an optical axis of the condensing lens whereon the light beams from the plurality of light sources are incident through respective positions on the condensing lens and diffracted into the light receiving section of the light guiding element. The mirror comprises a first mirror and a second mirror where the first mirror reflects the light beams from the light sources in a direction that intersects the optical axis of the condensing lens and the second mirror allows the light beams reflected from the first mirror to be incident into the condensing lens by directing the light beams in a direction parallel to the optical axis of the condensing lens. The first mirror is a conical internal-reflection mirror for reflecting the light beams from the plurality of light sources, and the second mirror is a conical external-reflection mirror for reflecting the light beams from the first mirror. The light guiding element mixes the light beams and reduces their coherence to flatten the light intensity distribution. The light guiding element needs to be long in order to mix the light beams from each source into a common light beam which can be used for projecting devices where the common light beam illuminates an optical gate where a light modulating object is positioned and where a projecting system is designed to image the optical gate and/or modulating object onto a target surface. The light sources are semi-conductor laser devices, producing relatively narrow and parallel light beams and the dimensions of the first and second mirror are much larger than the light beams. As a consequence the laser beams can thus be focused into the light guiding element, as the laser beams will be inside the first and second mirror. However in illumination devices it is desired to use ordinary LEDs which, however, as which due to etendue issues cannot produce as narrow and parallel light beams as laser devices. As a consequence there will be a large loss of light if the laser devices of EP 0978748 were replaced by ordinary LEDs, as a large part of the light reflected by the first reflector will not hit the second reflector due the fact the second reflector narrows down at the top of the cone. This light will not be reflected towards the converting lens by the second reflector. Alternatively EP 0978748 discloses that mirror and the condensing lens can be replaced by a concave mirror. Here, the light guide element is placed in such a manner that its optical axis coincides with the optical axis of the concave mirror and its light-receiving aperture is positioned at a focal point of the concave mirror. The embodiment results in a large light source unit as the concave mirror need to be much larger than the light beams, especially in the case where ordinary LEDs are used since as the light beams from these will be relative broad compared to a laser beam. Yet another issue is the fact that ordinary LED due to the manufacturing process typically are provided with rectangular dies and as a consequence the light guiding element needs to be event longer in order to mix the light beams properly.        
U.S. Pat. No. 6,830,359 discloses an illuminating or indicating device, including at least two light sources, each light source being associated with a first optical system where each first optical system, at finite distance, forms a real image of the light source, the images of the light sources being coincident at a common point constituting a secondary source, and a second optical system having an optical axis passing through the secondary source forms an illuminating or indicating beam from this secondary source. In one a variant the first optical systems forming real images of the light sources are portions of ellipsoids arranged in a corolla about the axis optical axis in such a way that their first foci coincide with the light sources and that their second foci are coincident with each other on the optical axis and with the object focus of the reflecting surface of the second optical system. The second optical system is adapted to image the secondary source at infinity from the common point. This illumination device is thus not usable in projecting systems where an image of a light modifier needs to be projected to a projecting surface. The second optical system is a convex reflecting surface carried out as a revolution of a parabolic profile. This revolution is arranged in such a way that its optical axis is coincident with the axis of symmetry with respect to which the light sources are arranged such that its focus is coincident with the secondary source. As a consequence, the light beams from different light sources will constitute different part of the common light beam rather than being mixed.
WO06027621 discloses a light engine for the delivery and reformatting of the output of a light source. The light engine has a light source and a first mirror for reflecting light from the light source towards a target. The first mirror has a first focal point. A polarizer is provided between the first mirror and its focal point. The light engine according may also comprise a second mirror having a second focal point and adapted to reflect light towards the first mirror. The first and second mirrors are hyperbolic, elliptical or parabolic and the shape of the light sources needs to match the shape of the target in order to create an energy efficient system. This is often not possible when using a spherical symmetric optical system, as LEDs, due the manufacturing process, typically are provided polygonal shaped especially rectangular shapes
In general the prior art fixtures try to increase the lumen output by adding as many light sources as possible. The consequence is, however, that the efficiency with regard to power consumption versus light output is very low. Furthermore, a large amount of light is lost as the prior art fixtures typically only couple a central part of the light of the light beams through the gate in order to provide a uniform illumination of the gate, which again reduces the efficiency. The available space in light fixtures is often limited and it is difficult to fit many light sources into prior art fixtures, for instance because the optical components associated with the light sources often take up a lot of space. Yet another aspect is the fact that color artifacts often appear in the output from fixtures having light sources of different colors.